THE OLDEST PENNSYLVANIAN CONODONTS FROM NORTHEASTERN OHIO

Traditionally, the oldest Pennsylvanian marine rocks in northeastern Ohio belong to the Lowellville Member, but as described by Slucher and Rice (1994) there is a still lower marine to brackish unit that they referred to informally as “Unit A.” Ironically, although somewhat patchy in distribution, this unit is actually more widespread than the Lowellville that it underlies. The thickness of Unit A ranges from as little as 0.3 m to more than 12 m and its base may come as close as 5 m to the interpreted base of the Pennsylvanian in the area and its base is more than 30 m below the base of the Lowellville where both are present and about 55 to 80 m below the more persistent Vanport Member.

Two surface samples from Columbiana County and two cores, one from Columbiana County and one from Jefferson County were available to us. This study is based on the surface samples and the Columbiana County core (#2678). The surface samples were limestones and calcareous shales, and the core was divided into 22 samples, most spanning two feet of core, nearly all of these were non-calcareous shales, but with minor amounts of calcareous shale, limestone, and ironstone. Shales were processed twice with varsol, and limestones and other carbonate rocks with buffered acetic or formic acid.

The surface samples are more normally marine than the core and are dominated by Idiognathoides with lesser numbers of Declinognathodus and Idiognathodus. The core samples yielded very few Idiognathoides and proportionally far more Idiognathodus with this biofacies interfingering with the Cavusgnathus-biofacies, a genus that was rare in the surface samples.